Ultimate goal of the root canal system obturation is to provide a hermetic seal that prevents reinfection of the canal and subsequent leakage of fluid and antigenic agents into or from the periradicular tissues.1 In today’s era, there is increasing demand for prompt, simple and efficient obturation technique, which increases efficient practice and results innegligible stress for patients and clinicians. With the widespread use of rotary NiTi instruments and matched-taper Gutta-percha cones, the single-cone obturation technique has become popular.2 In order to improve the marginal sealing properties of root canal system, hydrophilic root canal obturating systems have been introduced. A Bio-ceramic root canal sealer has been introduced, commercially known as Endosequence BC sealer (Brasseler USA, Savannah, GA). Endosequence BC Sealer is a premixed and injectable endodontic sealer, and its nanoparticle size sanctions it to flow into canal irregularities and dentinal tubules. It is hydrophilicand uses moisture in dentinal tubules to initiate and complete its setting reaction. In addition, no shrinkage occurs on setting, resulting in a gap-free interface between thegutta-percha, sealer, and dentin.3 The most recent obturating system is the Smart-Seal System which is composed of C-points and Smart-Paste Bio sealer. The C-points have been designed to expand laterally utilizing the inherent moisture present in the instrumented root canal space.4 The ReaSeal SE system consists of a self-etching methacrylate sealer and Resilon core material. It reduces the application steps of the original epiphany system, thus becoming a more operator friendly and bonds to both the Resilon core and radiculardentin through hybrid layers on both substrates leadingto a mono-block unit, which may prevent leakage andimprove the root strength.5-7 Canals have different configurations, and as a consequence of these features the quality of the filling of the root canal space may vary owing to the shape of the cross-section. Mauger et al8 stated that long oval canals are present in 80% of mandibular incisors. After preparation, the oval-shaped canals may leave uninstrumented and unfilled recesses which have the potential to promote leakage. Juhasz et al.9 reported that the root canal form influenced short-term sealing ability, and Wu and Wesselink10 demonstrated that uninstrumented recesses in oval canals were unfilled or incompletely filled by cold lateral condensation of gutta-percha. The problems associated with root fillings of oval root canals was discussed in a recent study by De-Deus et al.11 The sealing ability is a basic feature that needs to betested for every root canal filling material or technique. Varioustest methods have been described to evaluate the qualityof seal by such methods as dye penetration,radioactiveisotopes test,bacteria or bacterial metabolites leakagetest,electrochemical technique,and fluid filtration.12 However, the published reports often reach different oreven conflicting conclusions. As pointed out byWu andWesselink, there was a high level of variation in theseresults and it was difficult to draw firm conclusions as towhich filling technique or material was the best insealing the root canal system. It was suggested thatmore studies should be devoted to perfecting microleakagemethodology.13 These methods include dye penetration, spectrometry ofradioisotopes, fluoro-metric and electrometric methods, bacterial penetration and fluid transport model.12 Xu et al.discussed a new non-destructive model that measures theleakage of glucose molecules quantitatively by using aspectrophotometer. The aim of the present study was to evaluate corono-apicalmicro-leakage along root canal fillings using glucoseleakage model by comparing three matched-tapersingle-cone filling systems with cold Gutta-percha lateralcompaction technique using glucose leakage model atdifferent time intervals.
MATERIALS AND METHODS
One hundred fifty left and right mandibular incisors wereselected and autoclaved. Periapical radiographs of eachtooth were taken in both the buccolingual andmesiodistal planes. Teeth with oval-shaped canals wereselected only when the ratio of the long: short diameter was ≥2.5 at 5 mm from the apex (Wu &Wesselink 2001, De-Deus et al. 2006). Teeth presenting
with an isthmus, lateral and accessory canals, ormore than one canal were excluded from the sample. Therefore, only 90 mandibular incisors were classified as single oval-shaped canals and were stored in 10%neutral formalin. The crowns were cut with help of diamond disk belowthe cemento-enamel junction so that the length ofroots wasstandardized at 15 mm. The working lengthwas determined and the canals were instrumented by Pro-Taper NiTi rotary instrument (Dentsply Maillefer) to size F2 using the crown-down technique after which circumferential filling was done with 20#K File. The canalswere irrigated after using each file with 5 ml of 3% sodiumhypochlorite (NaOCl) solution using a syringe and 29-G needle (NaviTip; Ultradent, South Jordan, UT). After finishingthe instrumentation, the prepared canals were rinsedwith 5 ml of 17% ethylenediaminetetraacetic acid (EDTA)solution for 2 min followed by 10 ml distilled water asfinal irrigation to remove any traces of NaOCl.
Samples grouping and root canal obturation
After drying all canals with absorbent paper points, the samples were divided accordingto the obturation technique and materials into fourexperimental groups of 20 samples each and two controlgroups of 5 samples each. Samples in the negativecontrol group did not receive root canal fillings while inthe positive control group they were obturated with a single-cone Gutta-percha size 25/0.06 but without sealerplacement. In Group 1, AH Plus sealer was mixed according to themanufacturer’s instructions and applied into the preparedroot canal using a lentulo spiral size 25. A master Guttapercha cone of size 25/0.06 was coated with sealer andplaced into the root canal to the full working length. Lateral condensation was achieved using size 25/0.02standardized Gutta-percha cones and size 25/.04 fingerspreader (Dentsply Maillefer). Excess Gutta-percha wascut at the orifice level with a flame-heated hand pluggerand vertically compacted. In the other experimental groups (Single-cone obturationtechnique), each sealer was prepared and placed intoprepared canals according to manufacturer’s instructions. The tip of the matched taper cone (C-Points/Bio-Cearmic Impregnated Gutta-percha orRealSeal point) was dipped into the sealer and placedslowly in up and down motion until reaching the fullworking length. The coronal excess of the master conewas pre-cut to coronal orifice using a scissors at a predetermined length. In the RealSeal group, the coronal surface of theobturation was light cured after 5 min for 40 s. All sampleswere incubated for 1 week at 37°C and 95% humidity toallow complete setting of sealers.
The roots in the experimental and positive control groupswere coated with triple layers of nail varnish, except at thecoronal end and apical 1 mm of the root end. The roots inthe negative control group were entirely covered with nailvarnish. Microleakage along the root canal was evaluatedusing the glucose leakage model as described by Xuet al.5 The concentrations of leaked glucose (mg/dl)were measured after 1 day and then after 1, 2, 3, 4and 6 weeks with a Glucose kit (Glucose Liquid,Quimica Clinica Applicada S.A) in a spectrophotometer(Beckman Du 520, Coulter, Germany) at a wave lengthof 505 nm.
The results were statistically analyzed by Kruskal-Wallis andMann-Whitney tests. To compare leakage at different timeswithin each group, Freidman and Wilcoxon signed rankstests were used. All level of statistical significance was setat a P value less than 0.05.
The negative control group showed no detectable glucose leakage throughout the experiment while thepositive control group had immediate substantial glucoseleakage, which increased over time. This indicates thatthe seal of the glucose leakage system was effective andreliable. The mean values and statistical comparisons between theexperimental groups at each time interval are given inTable 1. After the 1st day onward, there were significantdifferences between the experimental groups (KruskalWallis test, P < 0.05). The results of the Mann-Whitneytest indicated that there was no significant difference between Groups 2 and 3 throughout the test period. Afterthe 1st day, the highest glucose leakage was observed in Group 1. After the 1st week, the lowest glucose leakage was observed in the 3rd Group. Starting from the 3rd weekonward, the lowest glucose leakage was observed in the Groups 2 and 3. Statistical comparisons between glucose leakage valueswithin each group are presented in Table 2. There wasa progressive and significant increase in the glucoseleakage values in all experimental groups (Friedman test, P < 0.05).
Table 1: Glucose Leakage at various time Intervals
Table 2: Time interval Related Glucose Leakage
In the present study, the leakage along root canal fillingswas measured by the glucose penetration method,which is simple and could give reliable quantitativeleakage measurements. In the presentstudy, glucose was selected as the tracer because it is of small molecular size (MW = 180 Da) and is a nutrientfor bacteria. If glucose could enter the canal from theoral cavity, bacteria that might survive root canalpreparation and obturation could multiply and potentiallylead to periapical inflammation. Glucose, therefore, was thought to be more clinically relevant thanother tracers used in microleakage tests. Quantitativeanalysis of leakage was possible by determining theconcentration of glucose in the apical reservoir thatleaked through the filled root canal.14 To determine the concentration of glucose, theenzymatic glucose oxidase method was chosen becauseit provided the ultimate degree of specificity and highsensitivity when compared with other methods, such ascopper or ferricyanide methods. With this method,glucose is oxidized by the enzyme glucose oxidase inthe presence of oxygen to gluconic acid with formationof hydrogen peroxide.15 Then in the presence of a peroxidase enzyme, achromogenic oxygen acceptor (4-aminoantipyrine andphenol) is oxidized by the hydrogen peroxide, resultingin the formation of a red product (oxidized chromogen). The quantity of this oxidized chromogen is proportionalto the glucose present initially in the first reaction, whichquantity is determined by spectrophotometry. With this model, it was possible to quantify theendodontic microleakage continuously over time. Theamount of microleakage was the cumulative value of leaked glucose.16 The reactivity of obturating materials with glucose could affect the results of the glucose leakage test. The results Shemesh et al. indicated that all materials used in the current study did not show glucose reactivity.17 The results of this study indicate that all obturationsystems allow variable degrees of glucose leakage. Mandibular incisors with single oval-shaped canals were used in the present study with the purpose of evaluating the quality of root canal sealing in canals in which difficulties with the anatomy could complicate the root filling procedure. The studies of Pucci & Reig (1944) and Mauger et al. (1988) reported the anatomical variety of those teeth. The problem regarding irregular-shaped canals has been investigated previously.11 The oval canal shape may make it difficult to clean and fill (Wu et al. 2001). De-Deus et al reported that the irregular canal shape may influence the filling quality negatively. Kersten et al. (1986) pointed out that cold lateral compaction gutta-percha had been widely used in root canal treatment, although quality may vary depending on the root canal shape.11
The glucose leakage values of AH Plus groups withlateral condensation technique weresignificantly higher at the end of the experimentalperiod. This might be explained by the fast setting andsubsequent polymerization shrinkage of AH Plus sealer,18 the lack of bonding between this sealer and Gutta-percha the low penetration ability of this sealer withinthe dentinal tubules19 and its hydrophobic property thatprevents good adaptation of to the incompletely dried canal.20 Least leakage is seen in group 2 and 3 attributed to many reasons. The SmartSeal system (Prosmart - DRFP Ltd.,Stamford, UK). The system consists of obturation points (C-points) containing a polyamide core with an outerbonded hydrophilic polymer coating and an accompanying sealer Smart-paste Bio. The endodontic points are designed to expand laterallywithout expanding axially by absorbing residual water from the instrumented root canal space and the naturallypresent moisture in the dentinal tubules.21 The innercore of Pro-points is a mix of two proprietary nylonpolymers: Trogamid T and Trogamid CX. The polymercoating is a cross-linked copolymer of acrylonitrile andvinylpyrrolidone which has been polymerised and crosslinkedusing allyl methacrylate and a thermal initiator. The lateral expansion of Pro-points is claimed to occurnonuniformly with the expand-ability depending on theextent to which the hydrophilic polymer is prestressed (i.e., contact with a canal wall will reduce the rate or extent of polymer expansion).4 Bio-ceramic impregnated Gutta-Percha and Endosequence Bio-Ceramic Sealer, owing to its hydrophilic property and nano-particle composition has also shown comparable microleakage to Smart-seal system. Bioceramicroot canal sealers also exhibit chemical bonding to root canal dentinwalls as well as its corresponding Bio-zeramic particle impregnated Gutta-Percha.22 Group 4 Resilon/RealSeal was expected to show less leakage in comparison but leakage was significantly higher than groups 2 and 3. Resilon is a polymer-based thermoplastic resin containingbioactive glass, bismuth oxychloride, barium sulfate, and radiopaque fillers.23 Many advantages of Resilon (SybronEndo, Orange, CA) have been reported, whichinclude reduction in post-endodontic leakage. This advantage has been attributed to the monoblock concept. Secondary monoblocks are those that have two circumferential interfaces, one between the cement and dentin and the other between cement and the core material. In a root canal the C factor can be more preponderant than 1000. Hence, any polymerizing endodontic sealer would be subjected to greater volume of polymerization stresses during the setting process, resulting in debonding and gap formation along the periphery of the root filling24 and thus can be a contributing factor for the increased leakage seen in this group. Therefore, inspite of the hydrophilic nature of Resilon, leakage was significantly more than other hydrophilic groups.
Hydrophilic groups have shown significantly lesser leakage as compared to the gold standard hydrophobic Gutta-Percha Obturation system. Furthermore studies would be required to assess the hydrophilic nature of the recent obturation systems.